What are lightning sprites?

If you've been following Hurricane Matthew in the news, you likely ran across reports about lightning sprites. Pictures show red streaks of light above the storm clouds of Matthew, a stunning sight. But lightning as we typically think of it comes down from clouds and is white, so what's the deal with these lightning sprites?

Lightning sprites occur as rare, super-strong, positively-charged lightning hits the ground. (Most lightning that hits the ground is negatively charged.) The cloud-to-ground lightning is so powerful that it breaks apart molecules in the atmosphere into ions, and the result is a collection of lightning sprites. The sprites' red color is likely the result of these ions colliding with molecules in the atmosphere, in much the same way solar particles and the atmosphere interact to create the northern and southern lights.